Introduction:

Power Doppler ultrasound (PDUS) is increasingly used to assess synovitis in Rheumatoid Arthritis (RA). Prior studies have shown correlations between PDUS scores and vessel counts, but relationships with immunopathology have not been described. This study investigated the presence of Th1, Th17 and TNFa producing CD4+ T cells in peripheral blood (PB), synovial fluid (SF) and synovial tissue (ST) from RA patients and related these data to PDUS scores of either single or multiple joints.

Methods:

PB mononuclear cells were isolated from healthy controls or RA patients and stimulated with PMA and ionomycin for 3 hours in the presence of Golgistop. Paired SF were analysed where available (n=21). ST was obtained at arthroscopic synovial biopsy from six RA patients. Synovial blood flow was evaluated by power Doppler (PD) signal at 10 metacarpophalangeal (MCP) joints, wrists and knee joints. PD signals were graded on a semi-quantitative scale from 0 to 3 (where 0 = no synovial flow; 1 < 25% signal within ST; 2 = 2550% signal; 3 >50% signal). Intracellular expression of IL17, IFNg, and TNFa was determined by multicolour flow cytometry. Serum, SF and fibroblast culture levels of vascular endothelial derived growth factor-A (VEGF-A) were assessed by ELISA.

Results:

Th17 cells and dual IFNg/IL-1263-expressing cells but not Th1 cells are increased in PB of RA patients vs. healthy controls. These cells are further enriched in both SF and ST relative to PB. The percentage of PB Th17 cells did not correlate with systemic parameters of disease. The percentage of Th17 cells, but not Th1 cells, in SF positively correlated with CRP (r=0.51, p=0.03) and local PDUS-defined synovitis (r=0.62, p=0.003), suggesting a specific role for Th17 cells in active synovitis in RA. Patients with high levels of IL-17+ CD4+ T cells in SF display increased levels of vascular endothelial growth factor-A (VEGF-A) in SF; this was not observed for IFNg+ T cells. The addition of IL-17 but not IFNg increased VEGF-A production by RA synovial fibroblasts in vitro.

Conclusion:

Our data demonstrate a link between the presence of highly inflammatory Th17 cells and RA disease activity assessed by PDUS scores, and offer a novel immunological explanation for the clinical observation that rapid joint damage progression occurs in patients with persistent positive PDUS signal. Furthermore, our findings highlight PDUS as a possible surrogate marker of Th17 cells, which may identify patients who would benefit from early, aggressive therapy, including IL-17 antagonists.